A known focused pinhole gamma detection device is the NanoSPECT/CT™, a.o. described in U.S. Pat. No. 7,199,371. This device comprises an object carrier, arranged to position an object to be examined (e.g. a small animal) in an object space and at least one detector having a detector surface and being sensitive to gamma-photons. A collimator is positioned between the at least one detector and the object space.
The collimator has a plurality of pinhole systems, each pinhole system having a plurality of pinholes with mutually non-parallel central lines, having a mutual distance d that is smaller than a distance d1 between any of the at least two pinholes of said pinhole system on the one hand and any pinhole of any other pinhole system on the other hand. Each pinhole system has a pinhole system field of view, that is seen by at least one of the pinholes of said pinhole system and that is composed of the fields of view of the plurality of pinholes. A common overlap of the pinhole system fields of view of the plurality of pinhole systems of the collimator defines a focus volume, that is seen by all pinhole systems.
The NanoSPECT/CT™ device has a collimator with up to four slabs, each having up to 10 pinholes, which are all focused, i.e. they all point toward the focus volume, or central field of view (CFOV).
A problem with this known device is that higher energy gamma radiation, such as positron annihilation radiation, penetrates the thinnest portions of the collimator, which portions are formed by the pinhole knife edges, to such a degree that image definition decreases unacceptably. In theory, this could be solved by decreasing the acceptance angle of the cones that lead toward the pinhole. However, this leads to a reduced CFOV and/or to a bulkier device, both of which is undesirable.